Technical Field
The present invention relates to an electric power steering control device which assists a steering power transmitted from a driver in a vehicle, and particularly relates to an electric power steering control device in which suppression of a noise and a vibration can be improved while a response capability is maintained in a low speed region.
Background Art
In a conventional electric power steering control device, a target current for driving a motor, which is responded to a handle operation of a driver so as to assist a steering power, is set, and a feedback control method, by which a difference between the target current and an actual motor current is reduced, is adopted. In the control method, a proportion-integration control means (PI control), in which a proportion term (P term) and an integration term (I term) are used in accordance with the difference between the target current and the actual motor current, is generally adopted.
Moreover, it is suggested that a gain of the proportion term (P term) and a gain of the integration term (I term) are varied in a high speed region and a low speed region, and the gain in the high speed region is larger than the gain in the low speed region, whereby a sound and a vibration generated by a steering system are prevented in the low speed region, and a steering response capability of the steering system is improved in the high speed region. In other words, it is suggested that the gain of the proportion term (P term) and the gain of the integration term (I term) are varied in accordance with a vehicle speed, a noise and a vibration, which are easily caused in the low speed region, are suppressed by reducing the gain, and the gain is increased in the high speed region, whereby a response capability is improved (for example, refer to Patent Document 1).